WASHINGTON — It’s long been known that America’s school kids haven’t measured well compared with international peers. Now, there’s a new twist: Adults don’t either.

In math, reading and problem-solving using technology — all skills considered critical for global competitiveness and economic strength — American adults scored below the international average on a global test, according to results released Tuesday.

Adults in Japan, Canada, Australia, Finland and multiple other countries scored significantly higher than the United States in all three areas on the test.

Beyond basic reading and math, respondents were tested on activities such as calculating mileage reimbursement due to a salesman, sorting email and comparing food expiration dates on grocery store tags.

Not only did Americans score poorly compared to many international competitors, the findings reinforced just how large the gap is between the nation’s high- and low-skilled workers and how hard it is to move ahead when your parents haven’t.

In both reading and math, for example, those with college-educated parents did better than those whose parents did not complete high school.

The study, called the Program for the International Assessment of Adult Competencies, found that it was easier on average to overcome this and other barriers to literacy overseas than in the United States.

Researchers tested about 166,000 people ages 16 to 65 in more than 20 countries and subnational regions.

The test was developed and released by the Organization for Economic Cooperation and Development, which is made up of mostly industrialized member countries. The Education Department’s Center for Education Statistics participated.

The findings were equally grim for many European countries — Italy and Spain, among the hardest hit by the recession and debt crisis, ranked at the bottom across generations.

Unemployment is well more than 25 percent in Spain and more than 12 percent in Italy. Spain has drastically cut education spending, drawing student street protests.

But in the northern European countries that have fared better, the picture was brighter — and the study credits continuing education.

In Finland, Denmark, and the Netherlands, more than 60 percent of adults took part in either job training or continuing education. In Italy, by contrast, the rate was half that.

As the American economy sputters along and many people live paycheck-to-paycheck, economists said a highly-skilled workforce is key to economic recovery.

The median hourly wage of workers scoring on the highest level in literacy on the test is more than 60 percent higher than for workers scoring at the lowest level, and those with low literacy skills were more than twice as likely to be unemployed.

“It’s not just the kids who require more and more preparation to get access to the economy, it’s more and more the adults don’t have the skills to stay in it,” said Anthony Carnevale, director of the Georgetown University Center on Education and the Workforce.

Education Secretary Arne Duncan said in a statement the nation needs to find ways to reach more adults to upgrade their skills. Otherwise, he said, “no matter how hard they work, these adults will be stuck, unable to support their families and contribute fully to our country.”